This application relates to circuitry for integrated circuits such as programmable logic array integrated circuits (“programmable logic devices”), and more particularly, to circuitry that allows integrated circuits and systems using such circuits to minimize standby power consumption due to transistor leakage currents.
Modern integrated circuits are often based on metal-oxide-semiconductor (MOS) technology. Such integrated circuits have numerous metal-oxide-semiconductor field-effect transistors (MOSFETs). As fabrication techniques improve, it becomes possible to fabricate MOSFETS and other circuit components with smaller critical dimensions. For example, it becomes possible to fabricate MOSFETs with shorter gates. These shorter-gate MOSFETs can have improved performance characteristics with respect to longer MOSFETs.
Excessive power supply voltages lead to large power requirements for the integrated circuit. The trend has therefore been to use lower and lower power supply voltages on successive generations of integrated circuits. Modern integrated circuits often have power supply voltages of only 1.0 or 1.2 Volts.
With a power supply voltage this low, it becomes necessary to reduce the threshold voltage of certain transistors to a low level to maintain transistor performance at an acceptable level, particularly in speed-critical applications. However, low-threshold shorter-gate transistors can exhibit high levels of leakage current when turned off. As a result, the standby power consumption of integrated circuits with large numbers of low-threshold shorter-gate transistors may be much larger than desired.
Previously-known techniques for addressing high standby power consumption have not been entirely satisfactory. For example, one approach that has been proposed involves shutting down the power supply voltage to large areas of the integrated circuit when those areas are not in use. While this approach may reduce standby power consumption, it may not always work. For example, certain integrated circuits such as programmable logic device integrated circuits have circuitry that is programmed by a user. Because the user can change the configuration of the logic on the device before the device is placed into service in a system, it is not generally known in advance which areas of the integrated circuit should be shut down by removing the power supply voltage.
A better way to reduce integrated circuit standby power consumption is therefore needed.